Stripper finger with air cushion

ABSTRACT

A stripping apparatus for stripping copy sheets from the surface of the xerographic drum without destroying the developed latent electrostatic image on the copy sheet and without contacting the drum surface. A stripping finger is mounted on a linkage which is supported from the machine frame to position the finger in close proximity with the drum surface. The finger has a tip portion which protrudes slightly past the point of tangency of the finger with the drum surface. Small apertures are formed at the bottom of the finger which is hollow and is in communication with an air supply to cause an air cushion to be formed under the finger. The finger floats on an air cushion which is maintained at a predetermined distance from the drum surface. By virtue of the position of the tip with the drum surface, stripping of the leading edge of copy sheets to be stripped from the drum surface is accomplished without contacting the drum surface. A tiny channel formed in the forward surface of the tip is in communication with the air supply and provides sufficient pressure to blow developer material away from the tip to maintain it in clean condition. The linkage is arranged to exert a pressure biasing action on the finger in the direction normal to the direction of drum movement.

United States Patent Norton et al.

[ Sept. 24, 1974 STRIPPER FINGER WITH AIR CUSHION [75] Inventors: JamesR. Norton, Rochester, N.Y.; Herbert F. Schmalzbauer, Chester, Conn.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Nov. 13, 1972 [21] Appl. No.: 306,238

Primary Examiner-Richard A. Schacher Assistant Examiner-Bruce H. Stoner,Jr.

[57] ABSTRACT A stripping apparatus for stripping copy sheets from thesurface of the xerographic drum without destroying the developed latentelectrostatic image on the copy sheet and without contacting the drumsurface. A stripping finger is mounted on a linkage which is supportedfrom the machine frame to position the finger in close proximity withthe drum surface. The finger has a tip portion which protrudes slightlypast the point of tangency of the finger with the drum surface. Smallapertures are formed at the bottom of the finger which is hollow and isin communication with an air supply to cause an air cushion to be formedunder the finger. The finger floats on an air cushion which ismaintained at a predetermined distance from the drum surface. By virtueof the position of the tip with the drum surface, stripping of theleading edge of copy sheets to be stripped from the drum surface isaccomplished without contacting the drum surface. A tiny channel formedin the forward surface of the tip is in communication with the airsupply and provides sufficient pressure to blow developer material awayfrom the tip to maintain it in clean condition. The linkage is arrangedto exert a pressure biasing action on the tinger in the direction normalto the direction of drum movement.

5 Claims, 5 Drawing Figures STRIPPER FINGER WITH AIR CUSHION Thisinvention generally relates to xerography, and, in particular to animproved apparatus for stripping a paper support material having anelectrostatically transferred toner image thereon from a movingphotoconductive surface.

In conventional xerography, a photoconductive surface is uniformlycharged and the charged surface then exposed to a light image of anoriginal to be reproduced. Under the influence of the light image, thecharge on the surface is selectively dissipated to produce what is knownas a latent electrostatic image. The charged latent image is developed,or made visible, by attracting oppositely charged toner particles whichare brought into close proximity to the plate surface, into the imageareas. The developed image is then generally transferred to a papersupport material and the image affixed thereto to form a permanentrecord of the original document.

The copy sheet is placed over the image bearing photoconductive surfaceand the backside of the sheet subjected to a spray of ionized air. Acharge is built up on the sheet having a magnitude and polaritysufficient to electrostatically attract the toner particles from thephotoconductive surface to the copy sheet. However, during transfer, acharge opposite to the charge found in the non-imaged areas on the drumsurface is induced in the paper causing the copy sheet to becomeelectrostatically tacked to the drum surface. Removal of the copy sheetand. the toner image loosely adhering thereto has long been a problem inthe xerographic art.

One of the best known and most widely used stripping devices is themechanical air puffer. The copy sheet is stripped from the surface byintroducing a stream of air between the copy sheet and the surface andthen allowing the sheet to fall away from the photoconductive surfacewhere it can be picked up by a transport belt or the like. While puffingdevices are satisfactory in some respects, they are not entirelyreliable in operation.

Another stripping device is an array of mechanical fingers which areactuated by an electrical signal into contact with the photoconductorsurface so as to contact the paper edge and wedge the edge away from thephotoconductive surface. Normally these stripping fingers are made outof plastic materials or are plastic coated to prevent scoring orabrading the photoconductive surface. It has been found, however, thatdue to contact with the drum surface that the fingers wear quicklyrequiring frequent replacement due to the fact that they cannot remainin their sharp configuration which is necessary for the wedging effect.An example of a mechanical stripping finger is described in US. Pat. No.3,578,859. The present invention is an improved stripping finger overexisting stripping fingers and in particular is an improvement overcopending application Ser. No. 247,064, filed Apr. 24, 1972, entitledStripper Finger and commonly assigned herewith.

It is therefore a primary object of this invention to improve apparatusfor removing an electrostatically tacked image bearing support materialfrom a moving photoconductive surface.

It is a further object of this invention to remove electrostaticallytacked copy sheet from a moving photoconductive surface without scoringor abrading the surface.

It is a further object of the present invention to effect greaterreliability in stripping copy sheets from photoconductive surfaces.

It is still a further object of the present invention to provide asimplified design and construction for a stripping finger which does notcontact the photoconductive surface. I

It is yet another object of this invention to prevent developer materialfrom accumulating on the tip of a stripping finger stripping copy sheetfrom a xerographic drum surface.

It is yet another object of the invention to produce an inexpensivemanufacture and assembly for mechanically stripping copy sheets from aphotoconductive surface.

These and other objects as well as other features of the presentinvention are attained by positioning a single elongated finger with oneof its surfaces close and nearly tangent to the drum surface and its tipprotruding beyond the apparent point of tangency. Spacing between thefinger and the drum surface is maintained by an air cushion and apreload against the finger by a spring force.

For a better understanding of the present invention as well as otherobjects and features thereof, reference is had to the following detaileddescription of the inven tion to be read in connection with theaccompanying drawings, wherein: 1

FIG. 1 iillustrates schematically a xerographic reproducing apparatusemploying a preferred embodiment of the paper stripping assemby of thepresent invention;

FIG. 2 is an isometric view of the stripping assembly of the invention;

FIG. 3 is a side sectional view of the stripping assembly shown in FIG.2;

FIG. 4 is plan view of the stripping assembly; and

FIG. 5 is an enlarged side elevation of the stripping assemblyillustrating the operation thereof.

For a general understanding of the illustrated copier reproductionmachine in which the invention is incorporated, reference is had to FIG.1 in which the various system components for the machine areschematically illustrated. As in all electrostatic systems such as axerographic machine of the type illustrated, a light image of a documentto be reproduced is projected onto the sensitized surface of axerographic plate to form an electrostatic latent image thereon.Thereafter, the latent image is developed with an oppositely chargeddeveloping material to form a xerographic powder image, corresponding tothe latent image on the plate surface. The powder image is thenelectrostatically transferred to a support surface to which it is fusedby a fusing device whereby the powder image is caused permanently toadhere to the support surface.

In the illustrated machine, an original to be copied is placed upon atransparent support platen P fixedly arranged in an illuminationassembly and image rays are projected by means of an optical system forexposing the photosensitive surface of a xerographic plate in the formof a drum generally indicated by the reference numeral 10.

The drum 10 is mounted upon the frame of the machine and is adapted torotate in the direction of the arrow at a constant rate. During thismovement of the drum, it passes a charging station A where a uniformelectrostatic charge is applied to the surface thereof. Next at anexposure station B exposure of the drum surface to the light imagedischarges the xerographic plate in a latent electrostatic image inimage configuration corresponding to the light image projected from theoriginal on the supporting platen. As the drum surface continues itsmovement, the electrostatic image passes through a developing station Cin which there is positioned a developer assembly. The developerassembly deposits developing material to the upper part of the drumwhereat the material is directed to cascade over the drum surface inorder to provide development of the electrostatic image. As thedeveloping material is cascaded over the drum surface, toner particlesin the development material are deposited on the surface to form powderimages.

The developed electrostatic image is transported by the drum to atransfer station D whereat a sheet of copy paper is moved at a speed insynchronism with the moving belt in order to accomplish transfer of thedeveloped image. There is provided at this station a sheet transfermechanism to the developed image on the drum at the station D.

After the sheet is stripped from the drum by a stripping assembly 20, aswill be described more fully hereinafter, it is conveyed to a fuserapparatus generally indicated by the reference numeral 15 where thedeveloped and transferred xerographic powder image on the sheet materialis discharged from the apparatus by a belt conveyor to a suitable pointfor collection externally of the apparatus.

Suitable drive means are arranged to drive the drum in conjunction withtimed exposure of an original to be copied, to effect conveying andcascade of toner mate rial, to separate and feed sheets of paper and totransport the same across the transfer station D and to convey the sheetof paper through the fuser apparatus in timed sequence to produce copiesof the original.

It is believed that the foregoing description is sufficient for thepurpose of this application to show the general operation of anelectrostatic copier using an improved stripping apparatus constructedin accordance with the invention. For further details concerning thespecific construction of the electrostatic copier, reference is made toUS. Pat. No. 3,301,126, filed Sept. 30, 1964, in the name of Osborne etal.

Referring now to FIGS. 2-5, the stripping assembly 20 is connected'tothe machine frame 21 and comprises a support member 22 on which ismounted a linkage assembly 24 carrying a stripper finger member 26 whichserves to strip a sheet of copy paper from the surface of thephotoconductive drum in a manner which will become more apparenthereinafter. Linkage assembly 24 comprises a four bar linkage havingspring members 32 and 34 secured to the support member 22 and supportmember 25 by means of screws 35 and plate members 37. A torsion springassembly 31 serves to urge the stripper finger 26 into contact with thedrum by applying a biasing force on linkage assembly 24. Mounted onsupport member 25 is stripper finger member 26, which has a strippingtip portion 27 extending therefrom. Stripper finger member 26 may bemade out of any suitable material, such as, metal, ce-

6 ramic, and mixtures thereof. A preferred material is Fotoceram, aregistered trademark of Corning Glass Works, Corning, NY.

In accordance with the invention tiny apertures 28 are formed insegemented portions 30 arranged in the upper surface of the stripperfinger member to effect an air cushion between the drum surface andfinger member. Stripper finger member 26 is supported on a rigid conduitmember 37 received in support member 25 which pivotally supports thestripper finger member on an axis through the conduit member. Connectedto conduit member 36 is a flexible tube'member 38 which is connected toa conduit member 41 received in support member 22. Conduit member 41 isconnected to a source of pressurized air (not shown). By thisarrangement, pressurized air is supplied to the apertures 28 formed inthe upper surface of stripper finger member 26 which causes an aircushion to be formed between the surface of the stripper finger memberand the drum.

It will be noted that a channel 45 is formed tip portion 27 of thestripper finger member. The purpose of channel 45 is to direct a jet ofair along the tip portion to remove any loose developer materialtherefrom.

In operation, the stripper finger member is supported on an air cushionat a distance ranging from between 0.0005 to 0.0015 inches during thestripping operation which is satisfactory for stripping most paperthickness and weights. The air cushion supports the stripper at auniform distance from the drum surface due to the action of the springs32 and 34, which serve to urge the stripper finger upwardly into contactwith the drum surface. Movement of the finger member normal to the drumis effected by pivoting on the axis through conduit member 32. The tipportion of the stripping finger member extends slightly beyond the pointof tangency to the drum surface. In this manner the tip strips theleading edge of the sheet from the drum surface.

It will be appreciated that the stripper finger does not contact thedrum surface during the stripping operation, but is held therefrom at adistance which may be adjusted by regulating the air pressure. It hasbeen found that pressure ranging from about 10-12 PSI work well. Thefinger will not damage or otherwise abrade the drum surface. Moreover,due to the pressurized air acting on the tip portion of the stripperfinger, residual toner normally left on the drum surface will notcollect on the tip portion which in the past has been responsible formis-stripping. In addition to these advantages, the stripping finger ofthe invention has the ability to strip skewed copy sheets from the drumsurface. The stripping finger of the present invention is a significantadvance in the copying, and in particular, is highly advantageous overthe existing stripping devices used in xerographic copying machines.

What is claimed is:

1. In a xerographic copying apparatus for producing multiple copieswherein each developed copy sheet is electrostatically tacked to amoving xerographic drum image bearing surface, an improved strippingapparatus for removing the tacked copy sheet with developed imagesthereon from the moving drum surface comprising:

a frame,

resilient linkage means arranged in parallelogram fashion pivotallysupported on said frame against the action of spring bias means,

a stripper finger member mounted on said resilient linkage means at adistance from a drum surface less than the thickness of each copy sheetto be stripped, said finger member having a tip portion extending in alinear direction slightly past a point of tangency with the drumsurface, said finger member further having an array of apertures formedtherein on one surface thereof facing the drum surface, and

air supply means providing low pressure air in communication with theapertures to cause an air cushion to be formed between the finger memberand the drum surface acting against said resilient linkage means andspring bias means to maintain uniform spacing therebetween during thestripping operation to enable stripping of the copy sheet with developedimages thereon by said tip portion without contacting the drum surface.

pressure ranges from about 10 to about 12 psi.

1. In a xerographic copying apparatus for producing multiple copieswherein each developed copy sheet is electrostatically tacked to amoving xerographic drum image bearing surface, an improved strippingapparatus for removing the tacked copy sheet with developed imagesthereon from the moving drum surface comprising: a frame, resilientlinkage means arranged in parallelogram fashion pivotally supported onsaid frame against the action of spring bias means, a stripper fingermember mounted on said resilient linkage means at a distance from a drumsurface less than the thickness of each copy sheet to be stripped, saidfinger member having a tip portion extending in a linear directionslightly past a point of tangency with the drum surface, said fingermember further having an array of apertures formed therein on onesurface thereof facing the drum surface, and air supply means providinglow pressure air in communication with the apertures to cause an aircushion to be formed between the finger member and the drum surfaceacting against said resilient linkage means and spring bias means tomaintain uniform spacing therebetween during the stripping operation toenable stripping of the copy sheet with developed images thereon by saidtip portion without contacting the drum surface.
 2. Apparatus accordingto claim 1 wherein said tip portion is formed with at least one channelin comMunication with the air supply means to prevent developer materialfrom sticking thereto.
 3. Apparatus according to claim 1 wherein saidtip portion is maintained at a uniform distance from the drum surfaceranging from about 0.0005 to about 0.0015 inches depending on copy sheetthickness.
 4. Apparatus according to claim 1 wherein said stripperfinger is pivotally supported on conduit means communicating airthereto.
 5. Apparatus according to claim 1 wherein said air pressureranges from about 10 to about 12 psi.